Method and apparatus for treating solids



March 3, 1953 J. E. MONTGOMERY METHOD AND APPARATUS FOR TREATING soups 2SI-IEETSSHEET l File d March 3, 1949 March 3, 1953 J. E. MONTGOMERY2,629,938

METHOD AND APPARATUS FOR TREATING SOLIDS Filed March 3, 1949 2SHEETSSHEET 2 Atty.

Patented Mar. 3, 1953 UNITED STATES PATENT OFFICE Y METHOD AND APPARATUSFOR TREATING SOLIDS John E. Montgomery, Baton Rouge, La., assignor toKaiser Aluminum & Chemical Corporation, a corporation of DelawareApplication March 3, 1949, Serial No. 79,345

12 Claims. 1

This invention relates to an improved process in a gas in the form of adense turbulent body resembling a boiling liquid.

In many industrial processes and operations,

'itis necessary to remove the water content of wet granular or,pulverulent solids before subjecting the material to further treatmentor before transporting the material, if processing is completed. This iscommonly accomplished by heating the material to dry the same byevaporation of a desired amount of the moisture content of such solids.The heating may often be accomplished by direct heat exchange whereinthe material is contacted with heated gases, such as stack gases, insuitable stationary vessels or preferably in rotary kilns to provide abetter degree of contact between the discrete particles of the solid andthe gaseous heating medium. In other instances due to reactivity of thematerial, or the desire to avoid contamination, indirect heat exchangeis utilized to effect drying of the wet solids. This may also beaccomplished in rotary drums or driers for agitating the solids therebypromoting more efiicient heat exchange, However, all such processes andapparatus have certain limitations in regard to temperature control. uniormity of temperature, and efficiency of heat transfer.

It is a primary object of the present invention to provide an improvedmethod and apparatus for effecting indirect heat exchange with finely-divided solids characterized by the facility of 7 close temperaturecontrol and uniformity of temperature in the material being heated.

A further object of the invention is to provide an im roved process andapparatus for effecting indirect heat exchange with ulverulent solids inwhich an optimum coefiicient of heat transfer is obtained and processingtime is substantially curtailed.

A more specific object of the invention resides in the provision of amethod for drying wet solids finely divided in regard to ultimateparticle size drying wet olids finely divided as to discrete particlesize characterized by means to maintain the solids in a fluidized state,and to cause the solids to fiow in contact with the heating surfaces ina restricted tortuous path between the locus of the feed and thedischarge point.

Another specific object is to provide apparatus for continuously dryingwet pulverulent solids wherein uniformity of 1 temperature, optimumtemperature control .and'reduction of drying time is realized, and inwhich a superiorcoeificient of heat transfer is .attained. I

A more specific. object of theinventionisto provide a method andapparatus for continuously .drying finely dividedwethydrated solidswhich contain both free moisture and combined water wherebysubstantially complete elimination of the free moisture content iseifected while avoiding any calcination or removal of water ofcrystallization.

A further specific object of the invention is to provide a method andapparatus for continuously drying wet solids of a desired range ofultimate particle sizes without the formation of an objectionableproportion of fines;

A further 'snecific object of the invention is to provide a method andap aratus for controlling the level of the fluent bed of solids within afluidizing zone relative to the heat transfer surfaces and thus toprovide a zone of substantial depth for disintegration of wet and lum yclods of material fed to-the apparatusprior to contactwith the heattransfer surfaces. I The improved process of the present inventiongenerally com rises fluidizing finely divided solids in a confined zoneby contacting with a continuous flow of gaseous medium at velocitiessufficient to maintain a dense turbulent body of solids, feeding finelydivided untreated solids to the zone, causing the fluidized solids toflow in a tortuous path through the confined zone from the infeed to thedischarge point thereof. heating the fluidized solids by indirect heatexchange while flowing in a tortuous path, and discharging the dried orheated solids from the zone at the end of the tortuous path.

Apparatus of the invention particularly suitable for carrying out theprocess herein disclosed generally comprises a vessel adapted to byindirect heat exchange wherein the surface presented for heat transferis enormous, due to direct heat exchange apparatus for continuouslyvessel, preferably above the level; of the body of surfaces.

3 solids, means for withdrawing treated finely divided solids in anothersection of the vessel and preferably located at the level of the body offluidized solids, baille mean extending downwardly from above the levelof fluidized solids into the lower portion thereof and separating thetwo sections of the vessel thereby causing the fluidized solids to flowin a tortuous path, and

a plurality of indirect heat exchange surfaces positioned within bothsections of the vessel and occupying a substantial portion oft'hetortuous flow path for heating the fluidized solids.

The method and apparatus further comprise,

as a preferred embodiment, the disposition of'the heat transfer surfaceswithin the vessel in such relationship that the flow of fluidized solidsin the heating zone is divided into a series of co n fined or narrowpassages in respect tothe tortuous path thereof through the vessel. Thisa rangement of the heat transfer surfaces, which preferably comprisetubes carrying a suitable fluid. heat exchange medium, provides. a meanswhereby the tortuously flowing material is at all times in intimate heatexchange relation with the heating medium. The heating tubes arepreferably arranged as a. plurality of closely spaced vertical banksextending longitudinally through both sections of the vessel and wellbelow the level of the dense turbulent body of fluidized solids. Thesebanks occupy a major portion of the transverse space within. the lowerportions of both sections of the vessel, thus dividing the tortuous flowof material into several narrow streams. On the other hand, however, thespacings between individual tubes in a given bank constitutecommunicating passages between. the streams and permit. lateral movementof fluidized. particles betweenv the several passages, thus eliminatingimpedance to movement of. particles and. increasing the number ofparticle contacts with heating surfaces per unit of time.

The. above described construction, and arrangements of the. apparatusand manner of effecting the process. providefor a close control oftemperature and a uniformity of temperature throughout the heating zone.An extremely high heat transfer coefficient, that is, a substantiallyinstantaneous heat transfer throughout the body of fluidized solids, iseffected because of the extremely rapid rate of circulation. or movementof the teetering bed of fluidized solids. The transfer of heat betweenthe fluidized solidsand the heat transfer surfaces is at a very highrate due to the innumerable contacts of particles in the everchangingbody of solids with the heating This is greatly augmented by reason ofthe plurality of restricted passages for the fluidized solids in thetortuous flow path through the heating zone formed by the arrangement ofthe heating tubes. Since the heat transfer surfaces are permanentlysituated withinthe fluent bed and. as a consequence of the highefliciency achieved in heat transfer, in a typical embodiment of theinvention only about one-tenth as much footage of heating tubes isrequired as in conventional driers of equal capacity.

Control of the temperature of the heat exchange medium within the tubesis easily attained, and accurate control of the temperature of thematerial being heated is thus provided by reason of the extremeagitation of the finely divided solids which causes immediate anduniform heat transfer. &

The invention is particularly applicable to the drying of wet hydratedfinely divided solids wherein it is desired to effect a completeelimination of the free moisture content, while avoiding any partialcalcination or removal of Water of crystallization. In view of the closetemperature control and uniformity of temperature attainable; any localoverheating and consequent partial calcinaticn is completely avoided.

An important and particularly advantageous feature of the method andapparatus applied to thedrying of solids is the provision of a coherentsolids disintegration zone within the fluidizing vessel.

Even relatively small amounts of free moisture, for example 8%, in thesolids charged to the fluidized solids drier causes the particles of thesolids to cohere in lumps or clods. This lumping or. cladding of themoist solids is markedly increased upon contact with heated surfaces,such as steam pipes and the like. This substantial consolidation ofsolids particles prevents proper disintegration of the solids into theirutimate size necessary for proper fluidization even' in the presence ofthe fiuidizing medium. These coherent lumps or clods harden andaccumulate on and between the. hot-surfaces. As a consequence of suchparticle consolidation, localized areas of the bedof fluidized solidsbecome immobilized and the remainder of the bed is subjected to greatdisturbance incident to passage of an. excessive volume of fluidizingmedium therethrough Ineffect, fluidizing. velocities in the mobile partsof the bed are exceeded, and apparent lifting velocities are set up,which cause excessive entrain-ment of solids in the gaseous fluid'mingmedium resulting in undue dust losses. The efficiency and capacity ofthe drier is adversely affected and quality of the drier product isimpaired.

Substantially completeelimination of this problem has been realizedbythe present invention when the charging stock consists of Wet coherentsolids having sufi'lcient moisture content to cause such consolidationof solids and isolating of parts of the heating surfaces. The fluidizedbed is maintained. at a depth within the vessel appreciably greaterthanthat of the heating surfaces. In other words, the level A (shown in Fig.i) of the bed offluidized solids is maintained at a height appreciablyabove the heating surfaces and the wet solids are fed to the topof thebed. Thus, the portion of the bed from the level I thereof to thetopmost heating surfaces constitutes a disintegration zone for the wetcoherent solids prior to contact with the heating surfaces.

In this disintegration zone the lumps or agglomerates of the wet solidsare effectively broken down into discrete particles due to the extremeagitation of the previously formed discrete particles in this portion ofthe fluidized bed. As flow of the fluidized solids progresses throughthe tortuous path, the particles move downwardly from the disintegrationzone into the zone occupied by the heating surfaces. In this manner, thedrier operates at optimum efliciency and capacity, and uniformfluidization throughout the solids bed is realized.

As the discrete fluidized particles are dried in heating zone, theyexhibit no tendency to reform coherent lumps or agglomerate.

Thus, the dried hydrated solids are discharged in the desired particlesize and are characterized by their free flow property. A specificillustration of this application is described herein below withreference to the drying of wet alumina trisolids over a wide range ofparticle sizes, for example, from a few microns to about mesh. However,the range of sizes for a given body of solids being treated is limitedby the particular gas velocity at which lifting or entrainment of thesmallest particles and fluidizing of the largest particles occur. Thisrange varies directly with increasing average particle size for solidsof'a given density. Suitable fluidizing gas velocities may be readilydetermined for solids of a given average particle size and density.

The method and the apparatus of the invention is described in greaterdetail with reference to the accompanying drawings which are merelyillustrative of a preferred embodiment of the invention and are not tobe construed as a necessary limitation thereof, in which,

Figure 1 is a side elevation of the fluidized solids heating vessel ordrier with parts broken away showing the top in vertical section;

Figure 2 is a top plan view of the vessel shown in Figure 1;

Figure 3 is an end elevation of the vessel shown in Figure 1;

Figure 4 is a side elevation of the heating tube banks and headers;

Figure 5 is an enlarged end elevation showing the heating tube banks andheaders;

Figure 6 is an enlarged fragmentary elevation with parts broken away ofa modified discharge arrangement for controlling the bed level.

Referring in particular to Figures 1, 2 and 3 of the drawings, the drieror heating vessel It! is shown as a vertical closed vessel of elongatedrectangular cross-section, which is provided with a bottom portion i I,preferably comprising a plurality of separated substantially tetrahedralgas chambers ll. Interposed between the vessel it and bottom I! is aperforated baffle or plate l2 extendingacross all of the gas chambersand provided with a plurality of small holes throughout its entire areathrough which the fiuidizing gaseous medium supplied to the chambers isuniformly and distributively introduced into the material or granularsolids being treated in vessel ID.

A gas or air inlet I3 is ositioned on one side of each of the gaschambers ll of vessel If] for the introduction into the system of thegaseous fluidizing medium under suitable pressure. Inlets 1-3 .are inturn connected to a gas manifold 34 through suitable pressure or gasflow regu- 1 lators 35 shown diagrammatically in Figure 1.

Thus, gas velocity or pressure may be independently controlled for eachgas chamber I I, whereby different gas velocities may be set up indifferent sections of the fluidizing vessel [0, if necessary, tomaintain uniform fluidization throughout the vessel.

As indicated above, the provision of the plu rality of gas chambers Hproves advantageous in affording a means for selectively controlling thepressure or gas velocity in various portions of the fiuidizing zone.However, the number of such units is determined in a large degree by thesize of the fluidizing zone and to some extent is dependent upon thetype of material treated. Vari- 4 ation in gas velocities in sections ofthe fluidizing zone are advantageous where changes in apparent densityof the fluidized solids occur, for example, as the material is dried.Further, the nece'ssity of disintegrating coherent wet solids in thefeed end of the zone, and the avoidance of tory results.

Valved discharge outlets 9 are provided at the bottom "or apex of eachgas chamber H for cleaning out pulverulent material such as fineswhich'may have passed downwardly through the holes in perforated baffle12, which is most likely to occur during shutdowns.

The top 14 of vessel 10 is provided with a feed inlet l5 for thematerial to be treated positioned near one end l6 of the vessel withrespect to its length. A double doored closure 36 hinged to the sides offeed inlet l5 may be-provided to prevent losses of dust and exit ofmoisture laden gases into the incoming feed. The closure is opened bythe weight of the feed and closed by coiled springs 31. An open overflowoutlet H for discharge of the treated solid material is located in theopposite end I 8 somewhat below the top of the vessel It). A tapereddischarge spout or duct I9 is fixed to the end 3 of the vessel at theoutlet I! to receive the treated material overflow for directing it toother treating apparatus, car loading apparatus or the like. In thisembodiment, the level of the fluidized body of solids is fixed by theposition of the overflow outlet l1.

The heating means, as shown in'Figure 1, and in detail in Figures 4 and5, comprises a plurality of vertical banks of heating tubes 20 extendingapproximately horizontally and longitudinally throughout the lowerportion of vessel in and positioned above the perforated plate or baflie12. As shown in Figures 1 and 4, a sufiicient number of banks areprovided to occupy a major portion of the space within the vessel bothlongitudinally and transversely. 1

Each bank of tubes 20 is connected to a vertica manifold 2| at one endthereof and a manifold 22 at the other end. The tubes 20 of adiacentbanks are vertically staggered for more efficient heat exchange with thesolids being treated.

It will be noted from Figure 4, that the banks of tubes divide the flowpath of the fluidized solids between infeed l5 and overflow outlet 11into a series of narrow elongated passages, which passages areintercommunicating between adjacent tubes in a given. bank throughouttheir vertical depth.

The manifolds 2] are "in turn attached a flanged header 23 located atthe top of the manifolds through which a suitable fluid heatin medium isintroduced. Manifolds 22 are provided with a discharge header 24 at thebottom of each for removal of the heat exchange medium. As shown inFigure 1, the entire heating assembly is positioned within vessel H1 ata slight angle to the horizontal, so that when a condensible gas, suchas steam, is utilized as the heating medium, the condensate will flowinto manifolds 22 thereby facilitating removal through discharge headeror condensate drain 24.

The vessel l c is advantageously compartmentized into two sections, 5and 6, by means of a vertical imperforate baffle 25 positionedtransversely between feed inlet l5 and overflow outlet ll. The bafile issupported by the sides 'of vessel l0 and extends across the entire widthof the vessel (as shown in Figure 2). Also, it extends from slightlybelow top 14 downwardly -vessel. through outlet 21. 'inthe drawings,outlet 2'! may connect. with a within: the vessel; to a point. aboutmidway through the: depth of the. heating tube. banks. Below the levelof the. tube banks, the. baiile 25 is provided withcut out portions orrecesses to receive theseveral banks of tubes'20- extending across thewidth of the vessel. A plurality of narrowbattle; extensions 26 are'thus formed which extend downwardly. between the heating tube banks.This construction causes the fluidized: material to flow throughsubstantially the 'entiredepth of the tube banks in its passage fromfeed section to-discharge section 6.

At the topll of vessel in, near end I8, a gas or; fluidizing' mediumoutlet- 2:! is provided through which moisture ladenair in the. casethe: use of the apparatus as a drier is. discharged.

.The gas. entering; section: 5 is discharged; over the topof. ba-me 25into. section B- and out of the Although not shown suitable dust.collector, such as a cyclone, to re-.

cover any entrained solids from. the fluidizing Covered manholesor'trapdoors 28 and 29 may be. provided in the top [4 of vessel [0, ifdesired, for periodic cleaning. or repair, if necessary. In

'addition, the vessel [0 may be provided with tubes 45 and- 4.6- forreception of thermocouples or other temperature measuring devices.

I In: the modification shown: in Figure 6 there is disclosed anarrangement for adjusting the locationv of the feed outlet. and in turnfor controlling the height of the fluent bed within vessel l0. Accordingto this embodiment, there is provided feed outlet opening 38 in walll8.- of vessel H! of substantially greater; depth than required forproper discharge of treated solids. Preferably the outlet 38- has: itsbottom or lowermost level corresponding to the lowest desired level forthe fluent bed, and has its uppermost level slightly above the highestdesired level for the fluent bed. An adjustable weir 39 is positionedacross opening 38 and is slidabl'y supported by brackets 40attached'to-wall l8. A threaded lug extending outwardly from weir- 39receives a threaded rod 42 supported from the top of duct [9 bymeans ofa nut or lug 43- and terminating in handwheel 44. Rotation of the wheelcauses the weir 39 to move up or down in outlet 38, thus, serving as ameans for controlling the height or the outlet; and in turn the heightof the fluidized bed within' the vessel. A discharge spout i s providedto receive the treated feed in the usual. manner.v

The operation of the apparatus will be described with reference to themethod of drying alumina trihydrate as it is received from'the flltersin a wet broken cake condition, even without substantial previousmechanical disintegra- I2 until the upper level is somewhat belowoverflow outlet 1 l forming a bed of appreciable depth. Steam or otherheating medium is continuously ,passed into the heating tubes 20 throughmani- .i.ol ds 2|. and header 23 and condensate or cooled -medinm isremoved through manifolds 22 and l 24.. Steainis preferred. indryingalumina.

4 at a sumcientpressure and velocity so that after dissemination throughthe perforations of plate I 2 the desired fluidity of the solids body isobtained, and a dense turbulent body of alumina hydrate through thedepth of the bed in both sections 5 and 6 results.

The baflle 25 prevents, the wet alumina hydrate which is continuouslyled to section 5 of vessel In at a rate. approximately equal to therate. of discharge of dried alumina hydrate through outlet l'l, fromvmoving toward the outlet until. it has moved downwardly between theheating tube banks dividing the flow into several narrow passages, whichare intercommuni eating between tubes 20 in the. banks. This provides acircuitous or tortuous flow passage of the wet alumina in a fluidizedstate through the major portion of the depth of the tube banks in bothsections 5 and 6, and insures a. complete drying before discharge fromoverflow outlet I1. I

It is desirable to maintain in section 5 a substantial fluidized bedabove tubes 20 so as to provide a disintegration zone or the like fordis integrating clods of alumina hydrate which may be fed to vessel It.-As previously pointed out the depth of the bed within sections 5 and 6is controlled by the location of feed outlet l1.

Ihe height of the fluent bed depends upon the height of disintegrationzone desired, which with many materials is generally influenced by theamount of free moisture present. High moisture content in the case ofalumina hydrate causes lumping and cladding. Thus, the modificationshown in Figure 6 is very useful where it is necessary to increase thedepth of the disintegration zone to accommodate a wet, sticky hydratefeed.

Thus, the fluidized alumina, as it dries, flows in a tortuous orcircuitous path downwardly in section 5, horizontally in the lowerportion of the bed underneath baffle 25, and upwardly in section 6 tothe overflow outlet ll, where it is discharged as dry alumina hydratecontaining less units of lineal movement per unit time.

than 0.1% free moisture. Due to minimizing of any local overheating thedried alumina hydrate contains less insoluble alumina, analyzing lessthan 0.03% insolubles, as compared to 0.07% for alumina hydrateprocessed in a conventional manner. Heat transfer coefficients of up toabout B. t. u./hr./so .ft. F. are obtained.

In the above-described utilization of the method and apparatus, it ispreferred to employ a gas velocity of 12 to 42 cubic feet per minute persquare foot of cross sectional flow area in order to maintain the bed ofalumina hydrate in a fluidized state of desired energy or agitation. Thegas velocity is thus expressed to eliminate consideration of changes ingas density due to temperature changes, which would be necessary ifvelocities were expresesd in the conventional Of course, the gasvelocity is subject to a wide range of values depending upon theparticle size, par ticle. shape, and the density of the material beingtreated, and in a typical alumina hydrate 9 V drying operation thefollowing conditions prevailed:

Fluidizing air:

Pressure at wind boxes 4 inches Hg Temperature at wind boxes 60-80 F.Flow 12,000 S. C. F./hour The degree of fiuidization, for example, ahigh energy or low energy bed, may suitably be controlled by varying thepressure of the fluidizing medium, or by providing a greater or lessernumber of perforations per square foot in plate I2 or by varying thediameter of such perforations, thus varying the gas velocity.Accordingly, it is possible to selectively control the velocity offiuidizing medium flowing through gas chambers II by utilizing one ormore of these modes of varying pressure.

For drying and heating other finely divided solids, the fluid heatingmedium may be gases other than steam, for example, stack gases, orpreferably other condensible gases, or it may be a heated liquid ormolten solid such as water, oil, melted sodium nitrate, and otherheating liquids, depending upon the temperature desired.

Also the preferred embodiment as shown in the drawings may be modifiedto include more than one baiile such as bailie 25. In such case, theadditional bafiie or baiiles are alternately positioned extendingdownwardly from slightly below the top I4 and upwardly from plate l2 ofvessel It, or as required, so that the material being treated is forcedto flow in a tortuous path successively through the several sectionsfrom the feed inlet compartment to the outlet compartment.

The method and apparatus of the invention provide an improved mean ofdrying or heating granular solids by indirect heat exchange and operatesat optimum efflcienoy of heat exchange through the several combinedfeatures thereof. The fluidizing of the solids permits rapid and uniformheating thereof in a manner similar to the eifect of agitation whileheating a liquid. The confined or tortuous path of flow of the fluidizedsolids over the heating tubes causing downward horizontal and upwardmovement ind restricted passages advantageously presents a maximum ofheating surface to the fluosolids without unduly restricting the freemovement thereof in vessel l0.

When the solids, such as wet alumina hydrate, are fed in the form ofbroken clods of filter cake onto the fluidized bed, they are quicklydisintegrated into discrete particles that mix with the other undergoingdrying.

Although the alumina hydrate drying operation as described herein isadapted to operate at atmospheric pressure, it is to be understood thatthe apparatus and method of the invention can be modified so as tooperate at pressures either above or below atmospheric.

Also, as previously mentioned, the method of the invention can becarried out by employing a gas other than air as the fluidizing medium.For example, gases which are adapted for creating inert or other specialatmospheres within the vessel may be employed, in which case it is gen10 erally desirable to compress them and recycle for further use.

In certain operations wherein the invention is used as a drier themoisture to be removed may be a solvent or the like which is desirablyrecovered. Such recovery may be effected by conventional recoverysystems.

I claim:

1. A method of drying wet solids which comprises establishing andmaintaining a dense turbulent bed of fluidized finely divided solids ina confined zone by passing a continuously flowing stream of gaseousmedium therethrough at a predetermined velocity, continuously feedingfinely divided solids into the bed of fluidized solids from a point insaid zone above the level thereof, causing the fluidized solidsconstituting the dense turbulent bed to flow in a restricted tortuouspath through said zone downwardly away from the point of infeed,laterally and then upwardly .toward a discharge point at the level ofthe bed, heating said fluidized solids by indirect heat exchange whileflowing in said tortuous path by passing the same in contact with aplurality of heat transfer sumaces positioned within the dense turbulentbed of solids, and continuously discharging the heated solids at the endof the upward portion of said tortuous path, while maintaining the levelor said fluidized solids bed substantially above the heat trans-.tersuriaces.

2. A method of drying finely divided solids which comprises establishingand maintaining a dense tunoiilent bed or iiuidized finely dividedsolids within a coniined zone by passing a continuously nowing stream orgaseous medi m tnei'ethroug'h at a predetermined velocity, continuouslyIGGCilIlg finely divided SOlluS into the bed of fluidized solids,causing the fluidized solids to how in a tortuous path downwardly awayfrom the point of inieeu, laterally and then upwardly toward a dischargepoint in said zone, dividing the now of solids into .a series of narrowintercommunicating streams Within the tortuous path, heating thefluidized solids by indirect heatexcnange while flowin in said narrowstreams in the tortuous path, and continuously discharging dried solidsIIOXI]. the zone at the end OI the upward portion of said path, thedischarge point in said zone being positioned substantially above theindirect heat exchange zone whereby the level of .the bed of fluidizedsolids is maintained substantially above the indirect heat exchangezone.

3. A method according to clami 2 in which the finely divided solids arecontinuously fed into the bed of fluidized sohds from a point in saidzone above the level of said bed.

4. A method according to claim 2 in which the flnely divided solids arecontinuously fed into the bed of fluidized solids from a point in saidzone above the level of said bed and in which the end of the upwardportion of the tortuous path is located at the level of the bed offluidized solids.

5. An apparatus for drying finely divided solids comprising a vessel ofelongated cross section adapted to hold finely divided fluidized solids,at least one gas chamber located at the bottom of said vessel, aperforated gas baiile interposed between said vessel and said chamberfor distributively introducing a fluidizing gaseous medium into thevessel to establish and maintain therein a dense turbulent body offluidized solids, an inlet for continuously feeding finely dividedsolids into said fluidized body positioned at one side of the vessel andabove the level of the solids, a discharge overflow outlet for treatedsolids dis- 11 posed in the vessel at the side longitudinally opposidesaid inlet and at the level of said body of fluidized solids, a battleextending downwardly from above the level of fluidized solids into thelower portion thereof and separating the vessel into communicating inletand discharge sections thereby causing the fluidized solids to flow in atortuous path, indirect heating means comprising a plurality of verticalbanks of tubes, said tubesof each bank being arranged in staggeredrelation to those of adjacent banks, said banks of tubes positioned at'adepth substantially below the level of said fluidized solids andoccupying a --substantial portion of the intermediate space within thetortuous flow path of said solids and dividing the same into a series ofrestricted passages intercommunicating between adjacent tubes in eachbank.

6. A method of drying wet solids of finely divided ultimatepanticlesi'zes which comprises establishing and maintaining a denseturbulent body of fluidized solids of a selected depth within a confinedzone by contactingwith a continuous flow of gaseous medium at fluidizingvelocity, causing said fluidized solids to flow in a tortuous paththrough said zone by partially dividing said zone between the infeed anddischarge .points thereof, heating said fluidized solids while flowingin said tortuous path-by contacting the same with a plurality of heattransfer surfaces in an intermediate portion of said flow path, feedingwet coherent solids into an upper portion of said body of fluidizedsolids, disintegrating the wet coherent solids into-finely dividedsolids in said upper portion of the body prior to contact thereof withsaid heating surfaces-and regulating the depth of the upper portion ofsaid body between the level thereof and the heating surfaces.

7. An apparatus according to claim in which a plurality of independentlyand selectively controlled gas chambers are positioned longitudinallyalong the bottom of said vessel.

*8. An apparatus according to claim 5 in which an adjustable weir meansassociated with the discharge overflow outlet is provided for regulating-the' level of the 'bodyof fluidizedsolids whereby --the'depth of saidbody above the heating tubes 'may'be selectively controlled.

-'9. An apparatus for drying finely divided we 'solids comprising avessel adapted to'holdfluidized finely-divided solids, means forintroducing "a fluidizin'g gaseous medium into the vessel to =esta'blishand maintain therein'a dense turbulent bed of fluidized solids, a baiilepositioned within the vessel extending-downwardly from abovethe level ofthe fluidized solids into the lower portion thereof, means for feedingfinely divided solids into the vessel on one side of said bafiie, meansfor discharging the dried finely divided solids from the vessel on theother side of said bafiie, :and indirect heat exchange means positionedin said vessel on both sides of said bafile, said indirect heat exchangemeans comprising plurality of banks of heating tubes, said banks oftubes being so disposed that a substantial portion of the space betweenthe feeding means and discharg means is divided into a series of narrowlaterally communicating passages, and said 'baflle having recesses inthe lower portion thereof to receive the upper portions of the tubebanks.

10. An apparatus for efiecting indirect heat exchange with finelydivided solids comprising a vessel adapted to hold finely dividedfluidized solids, means for introducing a fluidizing gaseous medium intothe vessel to establish and maintain therein a dense turbulent bed offluidized solids, a battle extending from above the level of thefluidized solids bed into the lower portion thereof and separating thevessel into communicating inlet and discharge sections, a dischargemeans positioned in the discharge-section and controlling the depth ofthe fluidized solids bed in both sections, means for feeding finelydivided solids into the vessel in the inlet section, and indirect heatexchange means positioned in said vessel in both sections and in thecommunicating space therebetween, said heating means in relation to thedischarge means being disposed substantially lower in said vessel tomaintain a substantial bed depth above the heating means in both theinlet and discharge sections.

11. A method for drying finely divided moisture-containing solids havinga tendency to'cohere and consolidate, which comprises feeding the solidsto a confined zone, fluidizing'the solids in said zone by passingtherethrough a-continuous flow of gaseous medium at velocitiestoestablish and maintain a dense turbulent bedof solids,disintegratingthe coherent solids portions of the feed into finely divided solids byagitation with the discrete particles of the fluidized solids bed in thefeed portion of said-zone, causing said finely divided fluidized solidsto flow in a tortuous path through the remainder of said 'zone, and

' heating the finely divided fluidized solids while flowing in saidtortuous path by contacting the same'with a plurality of heat transfersurfaces. 12. A method according to claim 11in which themoisture-containing solids are hydrated alumina.

JOHN E. MONTGOMERY.

REFERENCES CITED The following references'are of record in the file ofthis patent:

UNITED STATES PATENTS

